1. Field of the Invention
The present invention relates to heavy lids for sub-surface enclosures, and particularly to lids on pre-fabricated pits designed for use in servicing aircraft, etc. at docking, loading and refueling terminals.
2. Description of the Prior Art
Servicing of aircraft on the ground at modern aircraft terminals is frequently performed using pre-fabricated pits which are installed at aircraft docking, fueling and loading areas. The pre-fabricated pits are installed beneath the surface of the tarmac across which aircraft travel during docking, refueling and departure maneuvers. The pits are typically formed of fiberglass, steel or aluminum, and are constructed as enclosures with surrounding walls, a floor, and an access lid at the top of the walls. The pits are installed below the surfaces of loading and refueling aprons at aircraft terminals, remote parking locations and maintenance bases.
Pre-fabricated pits of this type are used to allow ground support functions to be carried out from sub-surface enclosures. These ground support functions include the provision of fuel, the provision of electricity to aircraft located in the docking area, the provision of air for cooling the aircraft interior and pressurizing air for starting engines of the aircraft, and for other aircraft support activities which are conducted on the ground. The use of sub-surface pits eliminates the need for mobile trucks, carts and other vehicles which are otherwise present in the loading area and which interfere with the arrival and departure of aircraft in the vicinity of the loading gate. The use of sub-surface pits allows the provision of fuel, power, cooling and pressurized air, and other supplies from a central location. The necessary fluid supplies and electrical power can be generated or stored with great efficiency at a central location, as contrasted with the conduct of such ground support functions from mobile generating or supply vehicles.
The sub-surface, pre-fabricated pits used for ground support functions typically house valves, junction boxes, cooling air terminations and other terminal equipment used to service aircraft that have been docked. Umbilical pipes and lines, otherwise stored within the pits, are withdrawn from the pits through hatches therein and are coupled to the docked aircraft to supply the aircraft with fuel, air for cooling the aircraft interiors, pressurized air for starting the engines and electrical power.
Pre-fabricated pits for this purpose are typically constructed with hinged, disk-like hatches within a larger lid. The hatches are ordinarily used to withdraw fueling lines and the like, and can be lifted using one hand. Both the hatches and lids must be constructed of heavy duty aluminum or steel, or some other strong material, as they must be able to withstand the weight of an aircraft as it rolls across the hatches.
As opposed to the smaller hatches, conventional lids which cover the entire top of the pit cannot be lifted manually even though it is quite desirable to have access to the complete enclosure of the pit for servicing faulty equipment, freeing fouled lines, and for performing other maintenance and repair functions in the pit. Heretofore, it has been necessary to employ a motorized lift or other machine to raise the lid of a sub-surface pit because the pit lids are too heavy to be lifted manually. Pits of the type described are constructed in various sizes, and lids having dimensions of four to eight feet by three to five feet are typical. Accordingly, very large forces are required to lift up the lid.